1. Field of the Invention
This invention pertains to a flip chip LED apparatus. More particularly, the invention relates to a flip chip structure of a light-emitting device comprising a UV/blue light emitting diode (LED) that is optimized to produce unique light output out of the bottom and focusing of that light to provide phosphor illumination, with high light extraction.
2. Discussion of the Art
Due to the discovery of UV and blue light emitting diodes (LEDs) of GaN-based epitaxial structures, it has become possible to generate white light from an LED by applying luminescent phosphor materials on top of the LED light output areas. These phosphor materials partially transform the UV or blue light of the GaN (gallium nitride), into longer wavelength light.
As used herein, the term xe2x80x9cUV/blue LEDxe2x80x9d means an LED emitting in the UV range, or in the blue range, or in both the UV and blue ranges of the electromagnetic spectrum.
The successful implementation of the device is dependent upon the efficient conversion of UV/blue light into visible light and the subsequent efficient extraction of the generated visible light from the device. Many techniques have been previously used to collect this light efficiently in the wire bonded non-flip chip format, but the wires and die metals and diffusions cause irregularities which cannot be effectively overcome in the non-flip chip embodiment. In this mode, a UV/blue LED emits light all over the LED structure, including the top, bottom, and sides, but not at the same intensities.
Thus, there is a particular need for an improved UV/blue LED structure having an efficient conversion and extraction of light out of the device producing white light.
There is a particular need for an improved GaN LED structure having an efficient conversion and extraction of light out of the device. The present invention optimizes light out the bottom of the LED structure in contrast to the traditional topside output from a prior art wire bonded LED structure. Motivation for the flip chip orientation is two-fold: First, in the flip chip orientation no bonding wires are present to obstruct the emission of light. Second, an optical model of the LED indicates that more light is emitted from the bottomside of the LED than from the topside.
Briefly, in accordance with one embodiment of the present invention, a semiconductor device formed in a flip chip structure is provided. The device comprises a substrate formed of a substantially transparent material. A semiconductor layer formed of gallium nitride is deposited on a top surface of the substrate. One or more layers of lensing material is deposited on a bottom surface of the device substrate. The lensing material is comprised of a polymer, an index matching material, or a mixture thereof.
A principal advantage of the present invention is that a UV/blue LED structure is disclosed that primarily enhances light output from the bottom and sides of the structure.
Still another advantage of the present invention is that lens materials and phosphor material can be applied to the bottom (sapphire/substrate side) surface of a flip chip die to direct the light from a flip chip UV/blue LED thus directing and gathering it.
Still a further advantage of the present invention is that an inexpensive structure is disclosed that is capable of obtaining uniform light from a UV/blue flip chip LED structure.
Still a further advantage of the present invention is that the performance of the semiconductor layer is optimized by depositing it on the top surface of the substrate in the form of one or more odd-sided polygons.
Still another advantage of the present invention is that an un-packaged UV/blue LED structure, to be used in a flip chip format, is disclosed that includes polymers applied to the bottom surface of the die that do not block the light in the blue or UV region of the spectra, but function as lenses and aid in light extraction by optimizing the optical indexes of the materials.
Still another advantage of the present invention is that an un-packaged UV/blue LED structure to be used in a flip chip format is disclosed that includes a polymer and monomer used as a solvent that is applied and cross-linked to the back of the LED die. The cross-linked material does not block the light in the blue or UV region of the spectra and may, additionally, be phosphor-filled to yield white light.
Still another advantage of the present invention is that phosphor and/or index matching materials are applied to the bottom and sides of a UV/blue flip chip LED structure to optimize light extraction and output.
Still a further advantage of the present invention is that an inexpensive assembly structure for LED technology is disclosed that uses flip chip technology and an optimized UV/blue LED device structure to emit light primarily from the bottom and sides of the die.
Still another advantage of the present invention is that a method of assembly for a UV/blue LED is disclosed which does not entail the use of a conventional lead cup frame assembly process.
Still another advantage of the present invention is that a UV/blue LED structure having enhanced optical characteristics is disclosed.
Still another advantage of the present invention is that novel frame assemblies incorporating the UV/blue LED of the present invention are provided.